clear all
clc
[ th , r ] = meshgrid ( ( 0 : 5 :360 ) * pi /180 , 0 : .05 :1 );
[ X , Y ] = pol2cart ( th , r ) ;
Z = X + i * Y; f = ( Z .^ 4 - 1 ) .^ ( 1 / 4 );
contour ( X , Y , abs ( f ) , 30 )
axis ( [ -1 1 -1 1 ] )
